The present invention relates to a positioning method for use in a magnetic disc apparatus, an XY stage and the like.
In the magnetic disc apparatus serving as an external storage unit of a computer, a magnetic head is moved to an intended track on the surface of a rotating magnetic disc to carry out recording/reproduction of data. In such a scheme, the magnetic head must be moved at a high speed and with high accuracy in order to improve the processing speed of data access. With a view to ensure stable positioning to a target track without overshoot in the procedure of track seek, a method is employed in which an orbit of a target position in the seek procedure is given and the difference between the present position of a head representing a control quantity and the target position is reduced by means of a controller, whereby the head is caused to reach the target position while being caused to follow a desirable position orbit. In that case, with the aim of reducing the difference between the head position and the orbit of the target position, application of acceleration feed-forward for causing the head to follow the target position orbit has been practiced in general. As an example, a method of generating a target position orbit and acceleration feed-forward is disclosed in JP-A-09-139032.
To perform fast positioning, it is important to apply an acceleration feed-forward current which causes the head to accurately follow a given target position orbit so as to be settled to the target position without error. But, when the moving time is shortened to such an extent that the acceleration/deceleration frequency of a drive pattern exceeds the frequency band of a control system, error compression based on following error feedback does not function sufficiently at the time that an orbit following error takes place, with the result that a retard response depending on a closed-loop characteristic of the control system is generated to degrade the capability of position settling. The influence of resonance of a positioning mechanism system acts as a main cause of the orbit following error. For example, in the existing apparatus, the primary resonance frequency of the positioning mechanism is 3 to 4.5 kHz. But, the required drive frequency is 3 kHz or more in the case of one track seek when the drive pattern is subjected to frequency conversion in terms of moving time. Accordingly, unless a primary resonance model of the positioning mechanism is taken into consideration, an orbit following error takes place.
An object of the present invention to provide a positioning control method for use in magnetic disc apparatus which can permit fast and stable settling to a target position without overshoot and undershoot in connection with a moving distance of one track seek to about 16-track seek for which positioning must be done within a moving time corresponding to the primary resonance frequency of the positioning mechanism.
To accomplish the above object, according to the invention, a method of generating a position/velocity orbit for reducing power at a specified resonance oscillation frequency possessed by the positioning mechanism, a method of generating acceleration feed-forward compensation capable of causing a head to accurately reach a target position even when a feedback system does not function under a condition that external disturbance does not act externally and a method of generating a position orbit corrected by a control target model inclusive of a resonance model of the positioning mechanism and specified accurately up to a moving frequency band are used in combination in a seek operation for moving the head to the target position to perform fast seek in connection with the moving distance of one track seek to about 16-track seek.